A linear motor is a motor which effects linear movement instead of rotational movement by linearly extending a structure of a rotary-type motor. In the case of the linear motor car, a magnetic field is induced by supplying alternating current to a primary coil mounted on a car side, and a force is generated due to an interaction between this magnetic field and a magnetic field induced on a secondary coil (reaction plate) mounted on a track side. This force is utilized as a motive force. A driving force for the motor car is thus obtained.
The reaction plate used as a secondary coil plate is required to have a property of low electric resistance. In view of the cost and the strength, a composite metal plate, which is obtained by overlaying a surface metal plate made of copper or aluminium upon a backing metal plate made of steel, is used.
Since the surface metal layer of the composite metal plate in which a high current flows through has a sufficient thickness of 2 to 8 mm, a mechanical bonding method such as calking, hot rolling bonding (hot bonding) and explosive bonding are conventionally used as a method for fixing the surface metal plate to the backing metal plate.
However, the mechanical bonding method such as calking requires an apparatus having a complicated structure thereby raising the manufacturing cost. Also, hot bonding or explosive bonding requires a large scale of manufacturing system thereby raising the manufacturing cost.
In this way, the cost of the secondary coil plate for linear motor car manufactured by conventional technique inevitably becomes high.